As compared with a liquid crystal display device, an organic light-emitting diode (OLED) display device has such advantages as self luminescence, rapid response, wide viewing angle, high brightness, beautiful color, and being thin and light, so it has been regarded a next-generation display technology. As a main structure of the OLED display device, an OLED substrate includes a plurality of pixel units defined by a pixel definition layer, and each pixel unit includes an OLED for emitting rays in a specific color. When manufacturing the OLED substrate, a film-formation method for forming the OLED mainly includes an evaporation manufacture process and a solution manufacture process. The evaporation manufacture process has been widely used in a small-size display device, while the solution manufacture process mainly includes inkjet printing, nozzle coating, spinning, and screen printing. Due to a high material utilization rate and being suitable for a large-size product, the inkjet printing technique has been regarded as an important way for the mass production of the large-size OLED display device.
However, the material for the inkjet printing must be dissolved in a solvent so as to form a solution for the printing, and then the solvent in the solution is evaporated by an evaporation process so as to form a film. During the printing, the solution is sprayed through a sprayer arranged above a display region of a display substrate. FIG. 1 shows the situation of the solution when it is evaporated. For the solution, the closer to a center of the display substrate, the stronger the atmosphere formed by the solution, the closer to a saturation state, and the more difficult the evaporation of the solvent thereunder. In addition, the closer to a peripheral region, the weaker the atmosphere formed above the display substrate by the solution, and the easier the evaporation of the solvent thereunder. Because the solution is dried at the peripheral region more rapidly, it will move toward the peripheral region during the drying. As a result, an uneven film will be formed in the pixel unit after the drying, and a display effect will be adversely affected.
In order to overcome the above defects, a commonly-used method is to add a peripheral printing region AA around the peripheral region, and the solution is also sprayed onto the peripheral printing region AA during the inkjet printing. Due to the existence of the solution at the peripheral printing region AA, a saturation region will be expanded to cover the whole display region, as shown in FIG. 2. However, the peripheral printing region AA cannot be used for display, i.e., it is equivalent to that a useless region is added between the original display region and the peripheral region where leads are arranged. In this case, a width of a bezel may be increased, so it is difficult to meet the requirement of a narrow bezel in the market. Hence, there is an urgent need to find an effective way so as to prevent the occurrence of an uneven film at the display region due to different atmospheres above the display substrate during the evaporation of the solvent when the film is formed by inkjet printing.